Electron density modulation in a pulsed dual-frequency (2/13.56 MHz) dual-antenna inductively coupled plasma discharge

Abstract

The electron density, n e , modulation is measured experimentally using a resonance hairpin probe in a pulsed, dual-frequency (2/13.56 MHz), dual-antenna, inductively coupled plasma discharge produced in argon-C 4 F 8 (90-10) gas mixtures. The 2 MHz power is pulsed at a frequency of 1 kHz, whereas 13.56 MHz power is applied in continuous wave mode. The discharge is operated at a range of conditions covering 3-50 mTorr, 100-600 W 13.56 MHz power level, 300-600 W 2 MHz peak power level, and duty ratio of 10%-90%. The experimental results reveal that the quasisteady state n e is greatly affected by the 2 MHz power levels and slightly affected by 13.56 MHz power levels. It is observed that the electron density increases by a factor of 2-2.5 on increasing 2 MHz power level from 300 to 600 W, whereas n e increases by only $20% for 13.56 MHz power levels of 100-600 W. The rise time and decay time constant of n e monotonically decrease with an increase in either 2 or 13.56 MHz power level. This effect is stronger at low values of 2 MHz power level. For all the operating conditions, it is observed that the n e overshoots at the beginning of the onphase before relaxing to a quasisteady state value. The relative overshoot density (in percent) depends on 2 and 13.56 MHz power levels. On increasing gas pressure, the n e at first increases, reaching to a maximum value, and then decreases with a further increase in gas pressure. The decay time constant of n e increases monotonically with pressure, increasing rapidly up to 10 mTorr gas pressure and at a slower rate of rise to 50 mTorr. At a fixed 2/13.56 MHz power level and 10 mTorr gas pressure, the quasisteady state n e shows maximum for 30%-40% duty ratio and decreases with a further increase in duty ratio.

Foundations of capacitive and inductive radio-frequency discharges

“…When two RF discharges are combined they are usually at different frequencies. Some examples of such combinations include hybrid discharges (a combination of an ICP or a helicon with a CCP) [2][3][4][5][6], dual ICP [7][8][9] and dual CCP. The latter is more commonly seen as a dual frequency CCP [10][11][12][13][14], i.e.…”

Electron and negative ion dynamics in a pulsed 100 MHz capacitive discharge produced in an O2 and Ar/O2/C4F8 gas mixture

“…Another technique for measuring absolute electron density, the microwave resonance probe (MRP), was reported previously [17]. This technique was successfully implemented in a variety of plasma systems and gas mixtures including Ar/O 2 /C 4 F 8 for measuring electron density in both the CW and time-resolved mode [18][19][20][21][22]. The combination of an MRP for measuring excess electron density produced during photo-detachment was also reported [23][24][25].…”

Measurement of electronegativity during the E to H mode transition in a radio frequency inductively coupled Ar/O2 plasma*

“…The microwave resonance probe tip is a "U-shape" structure, made of tungsten wire with 3 cm in length and 0.3 mm in diameter, and the distance of the two tips is 4 mm. The principle and the sensitivity of the microwave resonance probe, and the temporal resolution measurement of the microwave resonance probe system are detail introduced elsewhere, [31][32][33][34] and we will give a brief description here.…”